The present invention relates to wellhead equipment, and more particularly to a wellhead isolation tool for isolating a wellhead from the high pressures and the abrasive and/or caustic substances used in well treatment procedures.
It is not unusual for oil and gas wells to require stimulation to restart, or to improve, a flow of hydrocarbons from a hydrocarbon bearing formation. Such stimulation typically involves pumping fluid mixtures into the formation at high pressures. Such fluid mixtures often comprise acidic solutions and/or proppants that can be caustic and/or abrasive. Hydraulic fracturing, one common form of stimulating a hydrocarbon bearing formation, forces liquids and/or gasses which may include proppants or other abrasives therein into the formation. Extremely high pressures and high flow rates must be employed in the hydraulic fracturing process so that the proppants will be forced into the hydrocarbon bearing formation.
Conventional wellheads, commonly called well trees, are not generally designed to withstand the pressures and/or the abrasive or caustic nature of the substances required to stimulate a formation. Generally, the wellhead is designed to withstand pressures of less than about 5,000 psi. The substances utilized to stimulate the formation will be pumped into the well at pressures greatly exceeding 5,000 psi and may be as much as 20,000 psi.
There are a number of existing wellhead isolation tools that provide for the reciprocation of a mandrel through the wellhead into the well so that the substance utilized to stimulate the well passes through the mandrel and into the well without damaging the wellhead. However, because of the potentially dangerous nature of the well stimulation operation, there is a continuing need to provide a wellhead isolation tool which can be easily connected to the wellhead and disconnected therefrom, which provides easy access for connection of lines to supply the treatment fluid, and which provides an efficient and safe method to stimulate the hydrocarbon bearing formation.
The present invention is directed to a wellhead isolation tool for injecting substances through a wellhead into a tubular element, such as a production tubing, in a well. The wellhead isolation tool includes a tubular mandrel adapted to be received through a longitudinal passage defined by the wellhead. The tubular mandrel defines a mandrel flow passage and has a nonthreaded outer surface.
The wellhead isolation tool further includes at least one high pressure valve connected to an upper end of the tubular mandrel. Treatment substances such as fracturing fluids containing proppants and other treatment fluids may be communicated through the high pressure valve into the mandrel flow passage when the at least one high pressure valve is in an open position. The tubular mandrel has an upper position in which the mandrel does not extend through the wellhead into the well and a lower position in which a lower end of the mandrel is sealingly received in the production tubing in the well. A threaded drive rod for reciprocating the tubular mandrel is vertically aligned with the tubular mandrel and is connected to the at least one valve.
The wellhead isolation tool further includes a drive mechanism for vertically displacing the threaded rod to urge the tubular mandrel downward through the wellhead and into the tubular element in the well. Once the tubular mandrel is sealingly engaged in the well, treatment fluids can be flowed into the well at extremely high pressures through the tubular mandrel without damaging the wellhead. The wellhead isolation tool further includes a support structure which provides for the easy location and connection of the wellhead isolation tool to the wellhead.